Mega Froslass
Type: Ice/Ghost => Ice/Ghost
Item: Froslassite
Ability: Snow Cloak/ Cursed body => Charmmaker: gives 1.5x power to Fairy moves (Steelworker clone)
Stats:
HP : 70
ATK : 80
DEF : 70
SPA : 80 => 130 (+50)
SPD : 70 => 100 (+30)
SPE : 110 => 130 (+20)
New Moves: Nasty Plot, Aura Sphere
Description: Froslass becomes a very fast special sweeper, with good coverage moves in Charmaker-boosted Draining kiss, Psychic, Aura Sphere, Thunderbolt, and great STABs in Shadow Ball and Ice Beam/ Blizzard.
Mega Slowking
Type: Water/Psychic => Water/Psychic
Item: Slowkingite
Ability: Regenerator/Own tempo/Oblivious => Strong Will: halves the power of Ghost and Dark moves (Thick Fat clone)
Stats:
HP: 95
Atk: 75
Def: 80 => 120 (+40)
SpA: 100 => 135 (+35)
SpD: 110 => 135 (+25)
Spe: 30
New Moves: Stored Power, Stockpile
Descripton: Slowking is a very bulky special sweeper, with good defense-boosting moves in Stockpile and Calm Mind, while Stored Power abuses these boosts.
Mega Butterfree
Type: Bug/Flying => Psychic/Flying
Ability: Compound Eyes/Tinted Lens => No Guard
Item: Butterfrite
Stats:
HP: 60
ATK: 45
DEF: 50 =>
SPA: 90 => 130 (+ 40)
SPD: 80 => 95 (+15)
SPE: 70 => 115 (+45)
New Moves: Focus Blast, Fire Blast
Description: Tired of missing Hurricane, Fire Blast, Sleep Powder, and Focus Blast? Well, with Mega Butterfree, that's no longer a problem! With No Guard, Butterfree's Hurricane, Focus Blast, and Fire blast become really spamable, and a perfect accuracy Sleep Powder allows for a lot of setup opportunities.
Edit: changed froslass's ability